It is common for most conventional permanent-magnet generators to chop an electric current by using switching regulators, and so on to keep generated voltages within prescribed limits that can be tolerated by the electric equipment using that voltage. Nevertheless, very large power-transistors are needed to switch a high voltage and/or large current between a conducting “on” state and a blocking “off” state. This would cause an increase in generator dimensions, in a heat loss or energy dissipated in cooling and further in production cost. Moreover, the large power-transistors are more likely to raise any radio blackout or radio noise caused by excessive inrush current that would develop when chopping the electric current to keep the generated voltage within desired voltage limits. Thus, the shortcomings as stated just earlier will pose some very difficult problems for the large power-transistors.
In the commonly assigned Japanese Patent Laid-Open No. 2003-264996, there is disclosed a permanent-magnet generator with self-voltage controls, in which a winding is located outside the generator to produce a braking voltage in coils, keeping constantly the generated voltage within prescribed limits. U-phase, V-phase and W-phase windings to develop a three-phase alternating current are each connected at their terminals through switching means to the coils that have winding turns or loops set in a number of turns to maintain the generated voltage in the three-phase windings within acceptable limits. Terminals of the coils are in turn connected with any electric machinery. The coils are wound around a yoke in reverse directions to form the primary side of the transformer while other coils are wound around the yoke to form the secondary side and connected to an output terminal to deliver the voltage of the prescribed level.
Another commonly assigned Japanese Patent Laid-Open No. 2002-204556 discloses a motor-generator with magnetic flux controls in which there are provided three winding groups wound on teeth in a way differing in a number of turns from one another. The magnetic flux controller operates to make position control of a cylindrical member relatively to a stator core and switching control between series and parallel connections in response to rpm of a rotor, maintaining the generated voltage within the prescribed limits. With the magnetic flux controller operated as stated earlier, the high voltage occurs when the winding groups are connected in series while the low-voltage with large amount of current is given when the winding groups are switched into parallel connection. The high voltage is derived from a winding conductor that is so tapped on a split-winding wound around a stator core as to reduce the number of the winding turns as the rpm of the rotor rises. In the windings to develop the three-phase alternating current, subdivided windings 1U, 2U and 3U; 1V, 2V and 3V; and 1W, 2W and 3W are each connected in series at their connection points that are connected through lines to switches. The flux controller constructed as stated earlier, depending on the rpm of the rotor, makes angular position control of the semi-circular member with respect to the stator and also switching control of the wiring configuration between the parallel and series connections, thereby making it possible to provide the three-phase alternating electric source of the prescribed alternating voltage.
A further another commonly assigned Japanese Patent Laid-Open No. 2001-298926 discloses a generator with two voltage ranges switched from one to the other to match the desired voltage of the electric equipment using the voltage. With the prior generator recited now, a stator is comprised of an inside circular member lying radially apart from an outside circular surface of a rotor to leave a clearance between them, the inside circular member being made with teeth spaced away from each other in circular direction to form slots sequential in circular direction, an outside circular member surrounding around the tooth tips of the teeth raised radially above the inside circular member, two systems of stator windings either distributed-wound or concentrated-wound around the teeth with spanning across preselected slots, one of which contains low power windings less in the number of turns while another of which has high power windings more in the number of turns, and terminal lines having terminals connected to any preselected low power and high power windings. The stator windings either distributed-wound or concentrated-wound around any field pole corresponding to the rotor pole are split from the series connection into some parallel connections as the rpm of the rotor rises to regulate the generated voltage, so that the generated voltage is regulated by turning on and off the switches connected to their associated wirings connected with the terminals of the stator windings.
As recited earlier with referring to three commonly assigned senior patent applications, the present inventor has worked toward a resolution of issues in the prior permanent-magnet generators. In consequently, the permanent-magnet generator was developed in which a ring to control magnetic flux is placed between a stator and a rotor to move in circular direction relatively to the stator. Circular movement of the flux control ring with respect to the stator increases or decreases the clearance for the magnetic path between radially opposite teeth of the flux control ring and the stator, regulating the magnetic flux flowing towards the stator to keep the generated voltage within the prescribed range.
Nevertheless, the prior permanent-magnet generators developed so far are not quite good enough when they are used in the land vehicles including automobiles, and so on in which the rotor experiences wide variation in rpm ranging over the high speed to low-speed. Especially, there is a major issue under very low rpm of the rotor. The permanent-magnet generator, when associated with the automotive engine, would be suffered the variation in rpm ranging over from ten-fold up to fifteen-fold. Moreover, the permanent-magnet generators are needed to have a versatile generating capacity effective in wide operating conditions ranging over from idling to 7000 rpm and, therefore, it is not easy to keep the generated voltage within the preselected limits irrespective of operating condition of the automotive engine. Only the restricted clearance between the rotor and the stator in the prior permanent-magnet generators, however, was limited in regulating the magnetic flux of the permanent magnet. Thus, it still remains a major challenge to prevent the generated voltage from coming too low level even in very low rpm, continuing to maintain the voltage of the generator within a prescribed voltage limits.